Patent Document 1 describes an example of a method for fastening two types of differently shaped electromagnetic steel plates together to configure a rotor core adapted to be fixed to a rotary shaft of a rotating electrical machine by laminating the electromagnetic steel plates. The electromagnetic steel plates are fixed in a laminated state using, for example, a flanged tubular member. Specifically, a tubular member having a basal end in which a flange has been formed in advance is inserted through a fastening through hole of the rotor core. A ball having a diameter greater than the diameter of the fastening through hole is passed through the tubular member, thus expanding the tubular member. The distal end of the tubular member is then swaged in correspondence with the outline of the rotor core. The rotor core is configured by an inner member and an outer member, and coaxiality must be ensured between the inner member and the outer member. This makes it necessary to improve accuracy of the axes of the inner and outer members. According to a certain known method for fixing electromagnetic steel plates configuring a hollow rotor, for example, bolt insertion holes are formed in the electromagnetic steel plates, which configure a hollow rotor core. The electromagnetic steel plates are then fastened together using bolts and nuts to ensure cylindricity using axial fastening force.